Rockbox Graphical UI Design

Well i've decided i want to create my own theme and edit the graphics (ala boot logo/usb logo). With the help of t0mas and several other fellows on the IRC channel i've managed to learn how to use the CVS and devkit within a few hours, so give me a break if i get some things wrong here.

I actually managed to create a logo (test logo) and replace the USB logo in screens.c, but after looking at it in the simulater its come out very wrong. There could be a 100 reasons why its not working, so i'm going to start by asking exactly WHAT specifications rockbox needs the bmp's to be in.